The answer to your first question is 2, depending on what trunks (pstn/isdn/sip) will depend if you can get away with a os7200 exp can or need a os7400 exp cab.

Also depends on how many of those analog phones will go of hook at.the same time (unless you're using the 8/16sli3 or 8combo3 cards)

The 2nd question depends on what else you're running with those 480 sip phones. Most likely only 1 cabinet will be required though.